universe expansion logic ?


by hitchiker
Tags: expansion, logic, universe
Radrook
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#19
May8-12, 10:05 PM
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Quote Quote by Drakkith View Post
I don't believe matter is being fed from the observable universe to the unobservable universe.
Where is it all going from your standpoint then-tra la la land?


The border isn't a brick wall, its a barrier in time. Anything beyond that barrier CANNOT affect us yet. Objects just on the other side can and have been affecting objects on our side, we just haven't been able to observe this effect yet. Therefor we are not causally connected to it yet.


I never said that we are causally connected as human beings to anything that happens beyond that horizon. I never said that the horizon blocks all influences between these regions. Your misunderstanding is that you are focusing on people in relation to that horizon and I am talking about the two distinct regions themselves in relation to one another and people are totally irrelevant from the point of causality between these two areas.
bapowell
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#20
May8-12, 10:23 PM
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Quote Quote by Radrook View Post
1.Your last statement is self-contradictry and and places in serious doubt the reasoning ability of anyone who would express it. Are you aware of that or are you just jesting?

2. I never said that WE are causally connected as human beings to anything that happens beyond that horizon. Actually, and on second thought, after reviewing your blatantly self- contradictry statements , I decided that as far as I am concerned this discussion between us is over. Maybe when the arguments you present begin making at least a little bit of sense to me we might resume. Until then, no dice! This type of communication is extremely disagreeable. Yikes!
Your statements are confrontational and rude, Radrook. Drakkith is merely trying to engage in constructive discourse (the brick wall reference I'm sure was meant facetiously, as I know Drakkith to be a thoughtful commenter.) I'll advise you to read the PF rules on this kind of attitude -- this is a place to learn, not pick fights.
GeorgeDishman
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#21
May10-12, 06:17 AM
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Quote Quote by Chronos View Post
Radrook, keep in mind the unobservable universe is causally disconnected from the observable universe.
If we look back to z=6, we see galaxies as they were when the universe was about a billion years old. Those same galaxies can be seen from the other side at the same redshift by astronomers in galaxies far beyond our horizon. Thus can it not be said that parts of what we call the "observable universe" are causally connected to events we call "unobservable".
phinds
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#22
May10-12, 07:09 AM
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Quote Quote by GeorgeDishman View Post
If we look back to z=6, we see galaxies as they were when the universe was about a billion years old. Those same galaxies can be seen from the other side at the same redshift by astronomers in galaxies far beyond our horizon. Thus can it not be said that parts of what we call the "observable universe" are causally connected to events we call "unobservable".
Yes, it can. And it IS. Correctly.

Amounts of the universe beyond our current horizon WERE causally connected in the early universe (read about the CMB uniformity) but they are NOT at present.
hitchiker
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#23
May10-12, 09:15 AM
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Those same galaxies can be seen from the other side at the same redshift by astronomers in galaxies far beyond our horizon
redshift varies with distance, if you mean astronomers in galaxies that lies in our 'forward horizon' redshift would be much greater

it is like driving a car on highway.. horizon in front of you will become connected and rear horizon shrinks

we may never see more past as we can see now ,as everything is moving away from its origin forward
GeorgeDishman
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#24
May10-12, 12:40 PM
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Quote Quote by hitchiker View Post
redshift varies with distance, if you mean astronomers in galaxies that lies in our 'forward horizon' redshift would be much greater
I am talking of astronomers in a galaxy who observe the universe to be 13.7 billion years old as we do and at a co-moving distance of 57.5 billion light years from us. Call it "C".

The galaxy in the young universe, seen at a redshift of 7 by both the distant galaxy and us, is midway between C and us, call it "B". The causal connection from B to C is similar to that from B to us even though we consider B is observable but C is not.
phinds
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#25
May10-12, 12:45 PM
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Quote Quote by GeorgeDishman View Post
I am talking of astronomers in a galaxy who observe the universe to be 13.7 billion years old as we do and at a co-moving distance of 57.5 billion light years from us. Call it "C".

The galaxy in the young universe, seen at a redshift of 7 by both the distant galaxy and us, is midway between C and us, call it "B". The causal connection from B to C is similar to that from B to us even though we consider B is observable but C is not.
Yes, that's correct. Are you asking if the statement quoted here makes sense, or what?

EDIT: This response is based on "half-way". I did not consider the red-shift and I assume that hitchiker's comment below on the red shift is correct.
hitchiker
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#26
May10-12, 02:53 PM
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redshift 7 is within 14bly which is not halfway between C and us in your example
GeorgeDishman
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#27
May10-12, 06:11 PM
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Quote Quote by phinds View Post
Yes, that's correct. Are you asking if the statement quoted here makes sense, or what?
I was giving a counter-example to message #8 in this thread, posted by Chronos.

(Note that #8 is not equivalent to post #10, the latter is valid.)
GeorgeDishman
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#28
May10-12, 06:35 PM
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Quote Quote by hitchiker View Post
redshift 7 is within 14bly which is not halfway between C and us in your example
Ned Wright's cosmology calculator is very useful:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

Put in z=7 then press "flat". It will tell you that the comoving distance is 28.756 Gly. That's how far away the galaxy we can see is now.

I should perhaps clarify that what I mean by now is at a time in the history of the galaxy when the age of the universe determined from the CMBR is 13.7 billion years.

The page also tells you that the angular size distance is 3.5945 Gly. In a flat universe, that is how far away the galaxy was when the light was emitted (at that time, the age of the universe was 778 million years).

3.5945 * (z+1) = 28.756

Another galaxy equally far beyond it would also see that one at a redshift of 7 and would now be at a distance of 57.512 Gly.

Next, put in z=1089 which is the redshift of the surface from which we receive the CMBR and press "flat". The comoving distance is 45.647 Gly. That is the current location of the most distant matter we can see which is a fair candidate for being "the edge of the observable universe".

Sorry if I was too economical in my previous posts, hopefully this makes it clearer.
Drakkith
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#29
May10-12, 08:13 PM
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Quote Quote by GeorgeDishman View Post
I should perhaps clarify that what I mean by now is at a time in the history of the galaxy when the age of the universe determined from the CMBR is 13.7 billion years.
I like this view of time. Everyone, everywhere would measure the age of the CMBR to be the same correct?
hitchiker
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#30
May10-12, 11:40 PM
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Quote Quote by GeorgeDishman
Ned Wright's cosmology calculator is very useful:
thanks,
my calculation was wrong
Arifz
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#31
May11-12, 12:35 AM
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But, is there such thing as infinite in physics?
hitchiker
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#32
May11-12, 01:25 AM
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Quote Quote by Arifz View Post
But, is there such thing as infinite in physics?
only one thing is infinite, that is universe...the emptiness

physics is to deal with singularities like matter energy stuff like that which spawned out of nowhere in the emptiness

Bigger picture of universe go beyond physics
GeorgeDishman
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#33
May11-12, 02:07 AM
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Quote Quote by Arifz View Post
But, is there such thing as infinite in physics?
Temperature:

http://en.wikipedia.org/wiki/Negativ...y_distribution
GeorgeDishman
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#34
May11-12, 09:04 AM
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Quote Quote by Drakkith View Post
I like this view of time. Everyone, everywhere would measure the age of the CMBR to be the same correct?
Yes, by definition. It is also known as "cosmological time" or I like "comoving time":

http://en.wikipedia.org/wiki/Comovin...ng_coordinates


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